Chlamydia trachomatis is the most common sexually transmitted bacterial pathogen in the world, causing serious complications on women's reproductive health including ectopic pregnancy, pelvic inflammatory disease and infertility. C. trachomatis also causes infection of the eye resulting in inflammation and in some cases blindness. The objectives of this project are to define the epidemiology, risk factors, transmission kinetics, and pathogenesis of C. trachomatis infections in different population settings, including populations in resource constrained countries. We have used the Internet, www.iwantthekit.org, since 2004 to offer sampling in Maryland and other areas in the U.S. for chlamydia screening in over 6,400 women and over 3400 men using self-obtained vaginal swabs, penile-meatal swabs, and rectal samples. Samples are also tested for gonorrhea and trichomonas. Prevalence for chlamydia for women since 2004 is 7.2%, and for this year 5.9%. However the prevalence for chlamydia this year is 19.0% in young women age 15-19 yr. Both young age and Black race were statistically associated with chlamydia positivity. For men, the overall chlamydia prevalence has been 8.2%; for this year the prevalence is 6.8%. Acceptance for self-collecting penile and rectal swabs has been very high. Rectal chlamydia and gonorrhea prevalence this year for males in Maryland is 5.8% and 4.3%, respectively. Whereas for females in Maryland, rectal chlamydia and gonorrhea prevalence is 9.8% and 0%, respectively. To study the capability for performing a point-of-care self-test for trichomonas at home, we enrolled 92 women who performed the mailed test successfully at home, demonstrating high accuracy, high acceptability and trust in their result. Trachoma due to C. trachomatis infection is the most common cause of infectious blindness in the world. The WHO has recommended that three rounds of mass drug administration (MDA) with antibiotics be offered to control the disease in districts where the prevalence of follicular trachoma (TF) is >10% in children aged 1-9 years, with treatment coverage of at least 80%. We have conducted both surgical and antibiotic treatment intervention studies in Gambia, Niger, and Tanzania in efforts to control trachoma. To evaluate a point of care molecular diagnostic for field use we determined the sensitivity, specificity, and field utility of the Cepheid GeneXpert C. trachomatis assay for ocular chlamydia infection compared to Roche Amplicor assay. In a trachoma-endemic community in Kongwa, Tanzania, 144 children ages 0 to 9 were surveyed to assess clinical trachoma and had two ocular swabs taken. Of the 144 swabs taken the prevalence of follicular trachoma by clinical exam was 43.7%, and by evidence of infection according to Amplicor was 28.5%. The sensitivity of GeneXpert for C. trachomatis when compared to Amplicor was 100% and the GeneXpert test identified more positives in individuals with clinical trachoma than Amplicor. The GeneXpert test for C. trachomatis performed with high sensitivity and specificity and demonstrated excellent promise as a field test for trachoma control. Poling samples before testing has been demonstrated to be a cost effective method when prevalence in low. Positive pools can then be tested individually to determine the individual positive. When pools are negative all the samples in the pool are considered to be negative. This method will help with the cost of the trachoma elimination program. To determine whether infection recurs after mass treatment, we re-examined individuals in Tanzania five years after initiation of the MDA program. Treatment coverage was 80% for all ages in the first year. At five years, clinical trachoma rates were lower than at baseline, dropping to less than 45% compared to 81% at baseline. The prevalence of trachoma decreased in a linear fashion with number of years of mass treatment, and decreased prevalence of C. trachomatis infection was related to the extent of the previous years azithromycin coverage. In districts prioritized for three MDA rounds with very low baseline levels of trachoma, one round of MDA reduced active trachoma to low levels and chlamydia infection was not detectable in any community. There was no additional benefit to giving two further rounds of MDA. Programs could save scarce resources by determining when to initiate or to discontinue MDA based on testing for Ct infection, and one round of MDA may be all that is necessary in some settings to reduce TF below the elimination threshold. The source of infection following mass treatment is unknown. If migrants into a village undergoing MDA are shown to impede progress towards elimination, then a local strategy that addresses treatment of new families and a nationwide strategy that addresses migration will be needed. The purpose of this study was to quantify the effect of migrants on the prevalence of infection and clinical trachoma in communities. In four communities in Kongwa, Tanzania, all children were enrolled in a longitudinal study of infection and trachoma. New children were identified at census updates as having not been in the community at the previous census. Within communities, neighborhoods were defined as spatially close groups of households. All children in the communities were invited to be examined for trachoma, and have ocular swabs taken for evidence of infection. Trachoma was graded using the WHO simplified grading scheme, and swabs were processed using Amplicor. Children who were migrants were more likely to be infected and to have trachoma than children who were resident in the community, which was significant by the time of the survey following the third year of MDA (odds ratio, OR, 2.49, 95% confidence interval, CI, 1.036.05). The neighborhoods where newcomers resided were more likely to have infection a year later than neighborhoods with no migrants, which was most pronounced following the third year of MDA (OR 2.86, 95% CI 1.077.65). In summary, migrants to communities may be an important source of re-emergent infection, especially as MDA lowers infection among residents. Highly migrant populations may need a special surveillance and treatment program to avoid slowing progress in communities under MDA.